rattling, knocking noise

[jeepxj2007]

Alright, I have this noise on my xj, its coming from the bottom end somewhere, if you have the hood open you cannot hear it from the top end at all, the only time i ever notice it is when it is idling or very slow speeds with my head out the window 5 mph or less, goes away with rpms, doesn't increase in speed with rpms, i have great oil pressure, 60 at startup, once its warm around 40 ish under load and 35 at idle, it can only be heard down low by the front tires, i never really heard a rod knock or main bearing bad so i don't know what to listen for, i did try pulling one plug at a time, and that had no effect on the noise, sometimes putting it in drive and foot on the brake makes it go away, sometimes it doesn't, its just odd, i have no metal in my oil whatsoever, you cannont hear the noise if u rev it or increase rpms, i tried isolating the noise with a stethescope, but i can't really isolate it, i took a wooden rod and that worked better than the stethscope, i can a ting noise with the stethiscope on the oil pan, but i believe it is a timing chain issue because its not a kerplunk kerplunk type of thing but has a lot of time in the intervals and doens't soudn like a knock or anything, its more of a triangle music instrument type of noise and i don't believe it is bearing related, and the motor is suppose to only have 50,000 miles on it so i highly doubt it is bearing related, with all of this info does it sound like i have a serious engine prb or just a random noise jeeps make?...my dad told me its not a rod bearing and not to worry about it but i thought i would run it accross you guys, i know about the flexplate things, but i cannot get the bolts out cuz they are stuck good, but does it sound engine related or flexplate related?

 

[Beatjeep]

I have this same problem...anyone know what it is?

 

[5bucks]

I could be way off here, but I had a noise driving me nuts for 2 weeks that resembles in some respects what you describe. Mine ended up being the fan (belt driven) hitting the fan shroud. Mine only made noise when driving. On mine, one of the plastic tabs that hold the bottom of the fan shroud in place popped out allowing the fan to contact the shroud at certain rpms. I felt like a real schmuck when I figured out what was going on. Took 10 seconds to fix. Never picked up a tool. Just popped that tab back in place. Hope yours is that easy!

 

[Atl XJ]

You sure its not piston slap? That kinda sounds like what you're describing and its pretty common on the 4.0l. If thats what it is, I wouldn't worry about it too much, they'll usually run forever like that. My '95 has had it since 60k miles and its about to hit 130K miles with no bad side effects. It hasn't gotten any worse so I don't worry about it anymore. I drive my Jeep pretty hard too.

4.0ls are notorious for having a knock at idle.

 

[dizzymac]

I would get the inspection plate bolts out one way or another and check the flex plate, won't be a pretty sight if it lets go.

 

[Matthew Currie]

Check the flex plate just in case, and also check the water pump and the pulleys for play. But I agree that it could just be piston slap, especially if the sound doesn't seem to change with load and goes away when it speeds up. If so, don't worry. Also you do not specify the year. My 99 has a tricky evaporative emission system that includes a valve on the firewall which makes a knocking sound at idle. If you're not prepared, you'd swear there's a bearing about to go. It doesn't change much with engine speed, but it's just about the frequency that a bad bearing would rap at idle. If you have a later model, 97 or up, check that.

 

[jeepxj2007]

well i don't have a fan shroud, and this noise is bugging me, today i got down underneath and really listened with the stethescope, i couldn't really get the noise from the oil pan one time i thought i had it but i kept moving around and went back to it and it wasn't it, i took out the plugs in that general area and still nothing, its bugging me, and it randomly happens, not all the time, its weird, like when i first start it up i never hear it, does this sound engine related?...like serious engine problems or not?...i have good oil pressure and everythign, its just odd this is a 89 body, with 94 transfer case, tranny, and engine, it was in a roll over, it is supposed to be that, is there anyway I can tell to see if this is correct and I didn't just get cheated and its really a 89, but it has 280,000 on the odometer so id assume it would be running very poor and idling ruff, and burning oil and what not, which it doesn't, and everything was labeled from the engine swap, but how can i tell a 89 and a 94 apart?.....it is only suppose to have aroudn 50,000 on it, but anyways hopefully i don't have major problems

 

[nosigma]

I have the same "chucking noise" at idle, especially when hot. In my case it is piston slap. Before each wheeling trip (2-3 weeks apart) I drop in a bottle of STP to thicken the 20W-50 oil in motor and it goes away for a couple weeks. At 150k mi I use just enought oil that this works out pretty well. No real fix except to rebuild, no real harm until it opens up so much that you puke a ring, and that takes a long, long time on a low rev motor like the 4.0

John

 

[truckeejeeper]

Just throwing it out there.. have you checked the cat/exhaust connections?

 

[jeepxj2007]

I know for sure I have a exhaust leak, and i have rusted out holes everywhere in the exhaust, and the cat. looks like crap, all the metal mesh is gone and it looks to be on its last leg

 

[Matthew Currie]

well i don't have a fan shroud, and this noise is bugging me, today i got down underneath and really listened with the stethescope, i couldn't really get the noise from the oil pan one time i thought i had it but i kept moving around and went back to it and it wasn't it, i took out the plugs in that general area and still nothing, its bugging me, and it randomly happens, not all the time, its weird, like when i first start it up i never hear it, does this sound engine related?...like serious engine problems or not?...i have good oil pressure and everythign, its just odd this is a 89 body, with 94 transfer case, tranny, and engine, it was in a roll over, it is supposed to be that, is there anyway I can tell to see if this is correct and I didn't just get cheated and its really a 89, but it has 280,000 on the odometer so id assume it would be running very poor and idling ruff, and burning oil and what not, which it doesn't, and everything was labeled from the engine swap, but how can i tell a 89 and a 94 apart?.....it is only suppose to have aroudn 50,000 on it, but anyways hopefully i don't have major problems

If it is a 94 engine, does it have the 94 Chrysler fuel injection system or the 89 Renix system? If it's still wired as an 89 it will have the computer under the dash, and if it has the 89 manifolds as I think it must to work right, it will have an EGR valve and associated plumbing. The throttle bodies also differ, and a quick identifier is that the 89 throttle body has the vacuum connection for the MAP sensor (mounted to firewall) on the side, using a rather odd looking rubber double plug. The later version taps the vacuum from the manifold. If it is a fully endowed 94 the fuel injection computer will be on the left inner fender. There will be no EGR. The 89 would also have had a knock sensor on the side of the block down below the manifolds. If yours is a 94 block wired as an 89 they must have done something with that, either removing it or otherwise bodging it in to a block which lacks the boss for proper mounting.

If this noise is inconsistent and hard to trace, I'd look more closely at engine mounts and at the pulleys and the water pump (and of course at that flex plate if you haven't already). A bad engine mount could do something like this. So might a bad pulley or a loose water pump. Piston slap should be pretty regular and consistent, a sort of diesel-ish sound at idle especially when cold, disappearing at speed, and possibly when the engine is hot (the pistons expand and stop slapping). At least if you cannot track the sound to the pan, that's probably a good sign.

280K on the odometer does not automatically mean the engine would run badly. My 95 with 260K runs just fine, idles well and does not burn a bit of oil, although it does leak. In its present state, if it doesn't fall out of the rusty body, it could probably go another 100K miles with nothing but oil changes.

 

[Kreutz]

Piston slap should be pretty regular and consistent, a sort of diesel-ish sound at idle especially when cold, disappearing at speed, and possibly when the engine is hot (the pistons expand and stop slapping). At least if you cannot track the sound to the pan, that's probably a good sign.

That's exactly how mine sounds. Except it sounds like it's coming from the pan. It's not the flexplate. I had that checked. Any thoughts???
Thanks.

 

[jeepxj2007]

do you think i could of caused any damage by letting it idle with 20w-50 oil?, my moms jeep has it in hers and run fine, so i thought i would put it in mine, but it was't a knock, but a light rattle, so i never drove it anywere, no metal every popped up, it was getting oil because I coudl hear it draining after i shut off, but i just switched it out cuz i didn't think it woudl be very healthy, it idled for a max of 15 minutes

 

[Matthew Currie]

do you think i could of caused any damage by letting it idle with 20w-50 oil?, my moms jeep has it in hers and run fine, so i thought i would put it in mine, but it was't a knock, but a light rattle, so i never drove it anywere, no metal every popped up, it was getting oil because I coudl hear it draining after i shut off, but i just switched it out cuz i didn't think it woudl be very healthy, it idled for a max of 15 minutes

20W-50 shouldn't hurt it unless it was so cold the stuff didn't circulate, a bit unlikely in this season. I've found on my 95 that the piston slap seems a little quieter with thin oil than thick. Piston slap is not dependent on oil pressure, but on cylinder oiling and piston expansion. I haven't gotten too scientific about it all, but surmise that either the heavy oil has more shear strength and scrapes too much off the cylinder walls when it's cold, or perhaps it doesn't spray as well, or that light oil allows the pistons to heat up faster. Or of course it could all be in my head. There's a lot of junk in there.

 

[Biglead]

If you feel the knocking noise in the floor, check the stupid exhaust bracket that mounts to the front of the tranmission. The foot that clamps on to the exhaust breaks because its cheap. Mine is broken and clunking now and its the third time it has gone out on me. Now I am making one out of something heavier than stamped metal.

 

[dutchjeep]

He, I didn't know that there was supposed to be such a bracket? I think mine doesn't have it, and I too hear the slapping dieselish sound sometimes when the engine is cold. Also feel it on the inside. Where is that bracket supposed to be at, right after the manifold transitions to the exhaust pipe?

 

[camarors8992]

My 89 YJ knocks also. It's been like that for 5k miles with no problems. My rear main seals leak and it also has some blowby but it still runs with no problems. I'm also running 20w50 oil and it has almost stoped the blowby and has stopped the knocking some. I just let the motor warm up some before I go anywhere, I have to anyways because of gay carb.

 

[Biglead]

I own an 89 XJ and the bracket uses one of the bottom bolts on the front of the transmission to hold it to the Jeep. The other end looks like a foot where it is clamped to the exhaust tube. It doesn't fit very well and the dealer said it was a known problem and was fixed in later models. "Nice" I put a new one on last week and the noise is gone. I will take a picture of it and repost tonight. I am working on one that’s made out of thicker steel so it doesn't break again.

 

[90xj06]

by reading this post i found why when i turn off the engine it sounds like its peeing.

 

[partyinmuthafer]

I had the same exact problem.....turned out to be the cat!!!